Solid electrolytic capacitor containing an adhesive film

ABSTRACT

A capacitor comprising a solid electrolytic capacitor element that contains a sintered porous anode body, a dielectric that overlies the anode body, and a solid electrolyte is provided. The solid electrolyte contains an interior conductive polymer layer overlying the dielectric, an adhesive film that overlies the interior conductive polymer layer, which may be formed by sequential vapor deposition. An exterior conductive polymer layer also overlies the adhesive film.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims filing benefit of U.S. Provisional PatentApplication Ser. No. 62/657,174 having a filing date of Apr. 13, 2018,which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Solid electrolytic capacitors (e.g., tantalum capacitors) are typicallymade by pressing a metal powder (e.g., tantalum) around a metal leadwire, sintering the pressed part, anodizing the sintered anode, andthereafter applying a solid electrolyte. Intrinsically conductivepolymers are often employed as the solid electrolyte due to theiradvantageous low equivalent series resistance (“ESR”) and“non-burning/non-ignition” failure mode. Such electrolytes can be formedthrough solution phase polymerization of a liquid monomer (e.g.,3,4-ethylenedioxythiopene, EDOT) in the presence of an oxidant (e.g.,iron (III) toluene-sulphonate or iron (III) chloride) and a solvent(e.g., butanol). One of the problems with conventional capacitors thatemploy solution-polymerized conductive polymers is that they tend tofail at high voltages, such as experienced during a fast switch on oroperational current spike. In an attempt to overcome some of theseissues, premade conductive polymer slurries have also been employed incertain applications as an alternative solid electrolyte material. Whilesome benefits have been achieved with these capacitors in high voltageenvironments, problems nevertheless remain. For instance, one problemwith polymer slurry-based capacitors is that it is often difficult forthe interior polymer layers, whether in situ polymerized or made from apolymer slurry, to penetrate and uniformly coat the pores of the anode.Not only does this reduce the points of contact between the electrolyteand dielectric, but it can also cause delamination of the polymer fromthe dielectric during mounting or use. As a result of these problems, itis often difficult to achieve ultralow ESR and/or leakage currentvalues, particularly at relatively high voltages.

As such, a need currently exists for an improved electrolytic capacitorcontaining a conductive polymer solid electrolyte.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a capacitoris disclosed that comprises a solid electrolytic capacitor element thatcontains a sintered porous anode body, a dielectric that overlies theanode body, and a solid electrolyte. The solid electrolyte contains aninterior conductive polymer layer overlying the dielectric, an adhesivefilm formed by sequential vapor deposition that overlies the interiorconductive polymer layer, and an exterior conductive polymer layer thatoverlies the adhesive film.

In accordance with another embodiment of the present invention, acapacitor is disclosed that comprises a solid electrolytic capacitorelement that contains a sintered porous anode body, a dielectric thatoverlies the anode body, and a solid electrolyte. The solid electrolytecontains an interior conductive polymer layer that overlies thedielectric, an adhesive film that overlies the interior conductivepolymer layer, and an exterior conductive polymer layer that overliesthe adhesive film, wherein the adhesive film has a thickness of about 10nanometers or more and an intrinsic conductivity of about 1,000 S/cm ormore as determined at a temperature of about 25° C.

In accordance with yet another embodiment of the present invention, amethod for forming a solid electrolytic capacitor element is disclosed.The method comprises positioning a capacitor element with a reactorvessel, wherein the capacitor element comprises a sintered porous anodebody, a dielectric overlying the anode body, and an interior conductivepolymer layer overlying the dielectric; forming a film on the capacitorelement by a sequential vapor deposition process, the process includingsubjecting the capacitor element to a reaction cycle that includescontacting the capacitor element with a gaseous precursor compound thatbonds to a surface of the interior conductive polymer layer andthereafter contacting the capacitor element with a gaseous oxidizingagent to oxidize and/or polymerize the precursor compound; and applyingan exterior conductive polymer layer over the film.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE FIGURES

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figures in which:

FIG. 1 is a schematic illustration of one embodiment of a capacitor thatmay be formed in accordance with the present invention; and

FIG. 2 is a cross-sectional view of one embodiment of a sequential vapordeposition system that may be employed in the present invention.

Repeat use of references characters in the present specification andfigures is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

Generally speaking, the present invention is directed to a solidelectrolytic capacitor that contains a capacitor element including asintered porous anode body, a dielectric overlying the anode body, and asolid electrolyte overlying the dielectric. The solid electrolytecontains one or more interior conductive polymer layer(s) that overlythe dielectric, an adhesive film that overlies the interior layer(s),and one or more exterior conductive polymer layers that overly theadhesive film. The adhesive film typically has a thickness of about 10nanometers or more, in some embodiments from about 20 nanometers toabout 1,000 nanometers, and in some embodiments, from about 30nanometers to about 800 nanometers, and in some embodiments, from about40 nanometers to about 500 nanometers. Further, the film is formed bysequential vapor deposition of a conductive polymer, such as by atomiclayer deposition (ALD), molecular layer deposition (MLD), etc. Withoutintending to be limited by theory, it is believed that the use of suchsequential vapor-deposited conductive polymers in the adhesive film canprovide a variety of benefits to the resulting capacitor. For example,the capacitor may exhibit a high percentage of its wet capacitance,which enables it to have only a small capacitance loss and/orfluctuation in the presence of atmosphere humidity. This performancecharacteristic is quantified by the “wet-to-dry capacitance percentage”,which is determined by the equation:Wet-to-Dry Capacitance=(Dry Capacitance/Wet Capacitance)×100

The capacitor may exhibit a wet-to-dry capacitance percentage of about50% or more, in some embodiments about 60% or more, in some embodimentsabout 70% or more, and in some embodiments, from about 80% to 100%. Thedry capacitance may be about 30 nanoFarads per square centimeter(“nF/cm²”) or more, in some embodiments about 100 nF/cm² or more, insome embodiments from about 200 to about 3,000 nF/cm², and in someembodiments, from about 400 to about 2,000 nF/cm², measured at afrequency of 120 Hz and temperature of about 23° C. Capacitance may bemeasured using a Keithley 3330 Precision LCZ meter with Kelvin Leadswith 2.2 volt DC bias and a 0.5 volt peak to peak sinusoidal signal.

The ESR of the resulting capacitor may likewise be relatively low, suchas about 200 mohms or less, in some embodiments about 150 mohms or less,and in some embodiments, from about 0.1 to about 100 mohms, measured atan operating frequency of 100 kHz and temperature of about 23° C.Equivalence series resistance may be measured using a Keithley 3330Precision LCZ meter with Kelvin Leads 2.2 volt DC bias and a 0.5 voltpeak to peak sinusoidal signal. The unique nature of the adhesive filmcan also allow the solid electrolyte to better withstand a variety ofdifferent external conditions. Namely, the adhesive film generally has acompact structure that is relatively nonporous. In this manner, the filmmay be generally impermeable to oxygen and/or resistant to condensationof water vapor molecules, which can have an adverse impact on electricalperformance. For example, the capacitor can maintain good electricalproperties even under extreme conditions, such as at high humiditylevels, such as a relative humidity of about 40% or more, in someembodiments about 45% or more, in some embodiments about 50% or more,and in some embodiments, about 60% or more (e.g., about 60% to about85%). Relative humidity may, for instance, be determined in accordancewith ASTM E337-02, Method A (2007). The capacitor may, for instance,exhibit ESR values within the ranges noted above when exposed to thehigh humidity atmosphere (e.g., 60% relative humidity).

The capacitor may also exhibit a leakage current (“DCL”) of about 50microamps (“μA”) or less, in some embodiments about 40 μA or less, insome embodiments about 20 μA or less, and in some embodiments, fromabout 0.1 to about 10 μA. Leakage current may be measured using aleakage test meter at a temperature of 23° C.±2° C. and at the ratedvoltage (e.g., 16 volts) after a minimum of 60 seconds (e.g., 180seconds, 300 seconds). The dissipation factor of the capacitor may alsobe maintained at relatively low levels. The dissipation factor generallyrefers to losses that occur in the capacitor and is usually expressed asa percentage of the ideal capacitor performance. For example, thedissipation factor of the capacitor of the present invention istypically from about 1% to about 25%, in some embodiments from about 3%to about 15%, and in some embodiments, from about 5% to about 10%, asdetermined at a frequency of 120 Hz and temperature of about 23° C. Thedissipation factor may be measured using a Keithley 3330 Precision LCZmeter with Kelvin Leads with 2.2 volt DC bias and a 0.5 volt peak topeak sinusoidal signal. The capacitor may also be able to be employed inhigh voltage applications, such as at rated voltages of about 35 voltsor more, in some embodiments about 50 volts or more, and in someembodiments, from about 60 volts to about 300 volts. The capacitor may,for example, exhibit a relatively high “breakdown voltage” (voltage atwhich the capacitor fails), such as about 2 volts or more, in someembodiments about 5 volts or more, in some embodiments about 10 volts ormore, in some embodiments about 30 volts or more, in some embodimentsabout 60 volts or more, and in some embodiments, from about 80 to about300 volts.

Various embodiments of the capacitor will now be described in moredetail.

I. Capacitor Element

A. Anode Body

The capacitor element generally includes a dielectric formed on asintered porous body. The porous anode body may be formed from a powderthat contains a valve metal (i.e., metal that is capable of oxidation)or valve metal-based compound, such as tantalum, niobium, aluminum,hafnium, titanium, alloys thereof, oxides thereof, nitrides thereof, andso forth. The powder is typically formed from a reduction process inwhich a tantalum salt (e.g., potassium fluotantalate (K₂TaF₇), sodiumfluotantalate (Na₂TaF₇), tantalum pentachloride (TaCl₅), etc.) isreacted with a reducing agent. The reducing agent may be provided in theform of a liquid, gas (e.g., hydrogen), or solid, such as a metal (e.g.,sodium), metal alloy, or metal salt. In one embodiment, for instance, atantalum salt (e.g., TaCl₅) may be heated at a temperature of from about900° C. to about 2,000° C., in some embodiments from about 1,000° C. toabout 1,800° C., and in some embodiments, from about 1,100° C. to about1,600° C., to form a vapor that can be reduced in the presence of agaseous reducing agent (e.g., hydrogen). Additional details of such areduction reaction may be described in WO 2014/199480 to Maeshima, etal. After the reduction, the product may be cooled, crushed, and washedto form a powder.

The specific charge of the powder typically varies from about 2,000 toabout 800,000 microFarads*Volts per gram (“μF*V/g”) depending on thedesired application. As is known in the art, the specific charge may bedetermined by multiplying capacitance by the anodizing voltage employed,and then dividing this product by the weight of the anodized electrodebody. For instance, a low charge powder may be employed that has aspecific charge of from about 2,000 to about 70,000 μF*V/g, in someembodiments from about 5,000 to about 60,000 μF*V/g, and in someembodiments, from about 10,000 to about 50,000 μF*V/g. Such powders areparticularly desirable for high voltage applications. Of course, inother embodiments, high charge powders may also be employed, such asthose having a specific charge of from about 70,000 to about 800,000μF*V/g, in some embodiments from about 80,000 to about 700,000 μF*V/g,and in some embodiments, from about 100,000 to about 600,000 μF*V/g.

The powder may be a free-flowing, finely divided powder that containsprimary particles. The primary particles of the powder generally have amedian size (D50) of from about 5 to about 500 nanometers, in someembodiments from about 10 to about 400 nanometers, and in someembodiments, from about 20 to about 250 nanometers, such as determinedusing a laser particle size distribution analyzer made by BECKMANCOULTER Corporation (e.g., LS-230), optionally after subjecting theparticles to an ultrasonic wave vibration of 70 seconds. The primaryparticles typically have a three-dimensional granular shape (e.g.,nodular or angular). Such particles typically have a relatively low“aspect ratio”, which is the average diameter or width of the particlesdivided by the average thickness (“D/T”). For example, the aspect ratioof the particles may be about 4 or less, in some embodiments about 3 orless, and in some embodiments, from about 1 to about 2. In addition toprimary particles, the powder may also contain other types of particles,such as secondary particles formed by aggregating (or agglomerating) theprimary particles. Such secondary particles may have a median size (D50)of from about 1 to about 500 micrometers, and in some embodiments, fromabout 10 to about 250 micrometers.

Agglomeration of the particles may occur by heating the particles and/orthrough the use of a binder. For example, agglomeration may occur at atemperature of from about 0° C. to about 40° C., in some embodimentsfrom about 5° C. to about 35° C., and in some embodiments, from about15° C. to about 30° C. Suitable binders may likewise include, forinstance, poly(vinyl butyral); poly(vinyl acetate); poly(vinyl alcohol);poly(vinyl pyrollidone); cellulosic polymers, such ascarboxymethylcellulose, methyl cellulose, ethyl cellulose, hydroxyethylcellulose, and methylhydroxyethyl cellulose; atactic polypropylene,polyethylene; polyethylene glycol (e.g., Carbowax from Dow ChemicalCo.); polystyrene, poly(butadiene/styrene); polyamides, polyimides, andpolyacrylamides, high molecular weight polyethers; copolymers ofethylene oxide and propylene oxide; fluoropolymers, such aspolytetrafluoroethylene, polyvinylidene fluoride, and fluoro-olefincopolymers; acrylic polymers, such as sodium polyacrylate, poly(loweralkyl acrylates), poly(lower alkyl methacrylates) and copolymers oflower alkyl acrylates and methacrylates; and fatty acids and waxes, suchas stearic and other soapy fatty acids, vegetable wax, microwaxes(purified paraffins), etc.

The resulting powder may be compacted to form a pellet using anyconventional powder press device. For example, a press mold may beemployed that is a single station compaction press containing a die andone or multiple punches. Alternatively, anvil-type compaction pressmolds may be used that use only a die and single lower punch. Singlestation compaction press molds are available in several basic types,such as cam, toggle/knuckle and eccentric/crank presses with varyingcapabilities, such as single action, double action, floating die,movable platen, opposed ram, screw, impact, hot pressing, coining orsizing. The powder may be compacted around an anode lead, which may bein the form of a wire, sheet, etc. The lead may extend in a longitudinaldirection from the anode body and may be formed from any electricallyconductive material, such as tantalum, niobium, aluminum, hafnium,titanium, etc., as well as electrically conductive oxides and/ornitrides of thereof. Connection of the lead may also be accomplishedusing other known techniques, such as by welding the lead to the body orembedding it within the anode body during formation (e.g., prior tocompaction and/or sintering).

Any binder may be removed after pressing by heating the pellet undervacuum at a certain temperature (e.g., from about 150° C. to about 500°C.) for several minutes. Alternatively, the binder may also be removedby contacting the pellet with an aqueous solution, such as described inU.S. Pat. No. 6,197,252 to Bishop, et al. Thereafter, the pellet issintered to form a porous, integral mass. The pellet is typicallysintered at a temperature of from about 700° C. to about 1900° C., insome embodiments from about 800° C. to about 1800° C., and in someembodiments, from about 900° C. to about 1800° C., for a time of fromabout 5 minutes to about 100 minutes, and in some embodiments, fromabout 8 minutes to about 15 minutes. This may occur in one or moresteps. If desired, sintering may occur in an atmosphere that limits thetransfer of oxygen atoms to the anode body. For example, sintering mayoccur in a reducing or inert atmosphere, such as in a vacuum, inert gas,hydrogen, etc. The atmosphere may be at a pressure of from about 10 Torrto about 2000 Torr, in some embodiments from about 100 Torr to about1000 Torr, and in some embodiments, from about 100 Torr to about 930Torr. Mixtures of hydrogen and other gases (e.g., argon or nitrogen) mayalso be employed.

B. Dielectric

The dielectric may be formed by anodically oxidizing (“anodizing”) thesintered anode body so that a dielectric layer is formed over and/orwithin the body. For example, a tantalum (Ta) anode body may be anodizedto tantalum pentoxide (Ta₂O₅). Typically, anodization is performed byinitially applying a solution to the anode body, such as by dipping theanode body into the electrolyte. A solvent is generally employed, suchas water (e.g., deionized water). To enhance ionic conductivity, acompound may be employed that is capable of dissociating in the solventto form ions. Examples of such compounds include, for instance, acids,such as described below with respect to the electrolyte. For example, anacid (e.g., phosphoric acid) may constitute from about 0.01 wt. % toabout 5 wt. %, in some embodiments from about 0.05 wt. % to about 0.8wt. %, and in some embodiments, from about 0.1 wt. % to about 0.5 wt. %of the anodizing solution. If desired, blends of acids may also beemployed.

A current is passed through the anodizing solution to form thedielectric layer. The value of the formation voltage manages thethickness of the dielectric layer. For example, the power supply may beinitially set up at a galvanostatic mode until the required voltage isreached. Thereafter, the power supply may be switched to apotentiostatic mode to ensure that the desired dielectric thickness isformed over the entire surface of the anode body. Of course, other knownmethods may also be employed, such as pulse or step potentiostaticmethods. The voltage at which anodic oxidation occurs typically rangesfrom about 4 to about 400 V, and in some embodiments, from about 5 toabout 300 V, and in some embodiments, from about 10 to about 200 V.During oxidation, the anodizing solution can be kept at an elevatedtemperature, such as about 30° C. or more, in some embodiments fromabout 40° C. to about 200° C., and in some embodiments, from about 50°C. to about 100° C. Anodic oxidation can also be done at ambienttemperature or lower. The resulting dielectric layer may be formed on asurface of the anode body and within its pores.

Although not required, in certain embodiments, the dielectric layer maypossess a differential thickness throughout the anode body in that itpossesses a first portion that overlies an external surface of the anodebody and a second portion that overlies an interior surface of the anodebody. In such embodiments, the first portion is selectively formed sothat its thickness is greater than that of the second portion. It shouldbe understood, however, that the thickness of the dielectric layer neednot be uniform within a particular region. Certain portions of thedielectric layer adjacent to the external surface may, for example,actually be thinner than certain portions of the layer at the interiorsurface, and vice versa. Nevertheless, the dielectric layer may beformed such that at least a portion of the layer at the external surfacehas a greater thickness than at least a portion at the interior surface.Although the exact difference in these thicknesses may vary depending onthe particular application, the ratio of the thickness of the firstportion to the thickness of the second portion is typically from about1.2 to about 40, in some embodiments from about 1.5 to about 25, and insome embodiments, from about 2 to about 20.

To form a dielectric layer having a differential thickness, amulti-stage process may optionally be employed. In each stage of theprocess, the sintered anode body is anodically oxidized (“anodized”) toform a dielectric layer (e.g., tantalum pentoxide). During the firststage of anodization, a relatively small forming voltage is typicallyemployed to ensure that the desired dielectric thickness is achieved forthe inner region, such as forming voltages ranging from about 1 to about90 volts, in some embodiments from about 2 to about 50 volts, and insome embodiments, from about 5 to about 20 volts. Thereafter, thesintered body may then be anodically oxidized in a second stage of theprocess to increase the thickness of the dielectric to the desiredlevel. This is generally accomplished by anodizing in an electrolyte ata higher voltage than employed during the first stage, such as atforming voltages ranging from about 50 to about 350 volts, in someembodiments from about 60 to about 300 volts, and in some embodiments,from about 70 to about 200 volts. During the first and/or second stages,the electrolyte may be kept at a temperature within the range of fromabout 15° C. to about 95° C., in some embodiments from about 20° C. toabout 90° C., and in some embodiments, from about 25° C. to about 85° C.

The electrolytes employed during the first and second stages of theanodization process may be the same or different. Typically, however, itis desired to employ different solutions to help better facilitate theattainment of a higher thickness at the outer portions of the dielectriclayer. For example, it may be desired that the electrolyte employed inthe second stage has a lower ionic conductivity than the electrolyteemployed in the first stage to prevent a significant amount of oxidefilm from forming on the internal surface of anode body. In this regard,the electrolyte employed during the first stage may contain an acidiccompound, such as hydrochloric acid, nitric acid, sulfuric acid,phosphoric acid, polyphosphoric acid, boric acid, boronic acid, etc.Such an electrolyte may have an electrical conductivity of from about0.1 to about 100 mS/cm, in some embodiments from about 0.2 to about 20mS/cm, and in some embodiments, from about 1 to about 10 mS/cm,determined at a temperature of 25° C. The electrolyte employed duringthe second stage typically contains a salt of a weak acid so that thehydronium ion concentration increases in the pores as a result of chargepassage therein. Ion transport or diffusion is such that the weak acidanion moves into the pores as necessary to balance the electricalcharges. As a result, the concentration of the principal conductingspecies (hydronium ion) is reduced in the establishment of equilibriumbetween the hydronium ion, acid anion, and undissociated acid, thusforms a poorer-conducting species. The reduction in the concentration ofthe conducting species results in a relatively high voltage drop in theelectrolyte, which hinders further anodization in the interior while athicker oxide layer, is being built up on the outside to a higherformation voltage in the region of continued high conductivity. Suitableweak acid salts may include, for instance, ammonium or alkali metalsalts (e.g., sodium, potassium, etc.) of boric acid, boronic acid,acetic acid, oxalic acid, lactic acid, adipic acid, etc. Particularlysuitable salts include sodium tetraborate and ammonium pentaborate. Suchelectrolytes typically have an electrical conductivity of from about 0.1to about 20 mS/cm, in some embodiments from about 0.5 to about 10 mS/cm,and in some embodiments, from about 1 to about 5 mS/cm, determined at atemperature of 25° C.

If desired, each stage of anodization may be repeated for one or morecycles to achieve the desired dielectric thickness. Furthermore, theanode body may also be rinsed or washed with another solvent (e.g.,water) after the first and/or second stages to remove the electrolyte.

C. Pre-Coat

Although by no means required, an optional pre-coat may overly thedielectric layer so that it is generally positioned between thedielectric and the solid electrolyte. The pre-coat may include, forexample, an organometallic compound, such as those having the followinggeneral formula:

wherein,

M is an organometallic atom, such as silicon, titanium, and so forth;

R₁, R₂, and R₃ are independently an alkyl (e.g., methyl, ethyl, propyl,etc.) or a hydroxyalkyl (e.g., hydroxymethyl, hydroxyethyl,hydroxypropyl, etc.), wherein at least one of R₁, R₂, and R₃ is ahydroxyalkyl;

n is an integer from 0 to 8, in some embodiments from 1 to 6, and insome embodiments, from 2 to 4 (e.g., 3); and

X is an organic or inorganic functional group, such as glycidyl,glycidyloxy, mercapto, amino, vinyl, etc.

In certain embodiments, R₁, R₂, and R₃ may a hydroxyalkyl (e.g., OCH₃).In other embodiments, however, R₁ may be an alkyl (e.g., CH₃) and R₂ andR₃ may a hydroxyalkyl (e.g., OCH₃).

Further, in certain embodiments, M may be silicon so that theorganometallic compound is an organosilane compound, such as analkoxysilane. Suitable alkoxysilanes may include, for instance,3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane,3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane,3-(2-aminoethyl)aminopropyltrimethoxysilane,3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane,3-mercaptopropylmethyldimethoxysilane,3-mercaptopropylmethyldiethoxysilane, glycidoxymethyltrimethoxysilane,glycidoxymethyltriethoxysilane, glycidoxymethyl-tripropoxysilane,glycidoxymethyltributoxysilane, β-glycidoxyethyltrimethoxysilane,β-glycidoxyethyltriethoxysilane, β-glycidoxyethyl-tripropoxysilane,β-glycidoxyethyl-tributoxysilane, β-glycidoxyethyltrimethoxysilane,α-glycidoxyethyltriethoxysilane, α-glycidoxyethyltripropoxysilane,α-glycidoxyethyltributoxysilane, γ-glycidoxypropyl-trimethoxysilane,γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyl-tripropoxysilane,γ-glycidoxypropyltributoxysilane, β-glycidoxypropyltrimethoxysilane,β-glycidoxypropyl-triethoxysilane, β-glycidoxypropyltripropoxysilane,α-glycidoxypropyltributoxysilane, α-glycidoxypropyltrimethoxysilane,α-glycidoxypropyltriethoxysilane, α-glycidoxypropyl-tripropoxysilane,α-glycidoxypropyltributoxysilane, γ-glycidoxybutyltrimethoxysilane,δ-glycidoxybutyltriethoxysilane, δ-glycidoxybutyltripropoxysilane,δ-glycidoxybutyl-tributoxysilane, δ-glycidoxybutyltrimethoxysilane,γ-glycidoxybutyltriethoxysilane, γ-glycidoxybutyltripropoxysilane,γ-propoxybutyltributoxysilane, δ-glycidoxybutyl-trimethoxysilane,δ-glycidoxybutyltriethoxysilane, δ-glycidoxybutyltripropoxysilane,α-glycidoxybutyltrimethoxysilane, α-glycidoxybutyltriethoxysilane,α-glycidoxybutyl-tripropoxysilane, α-glycidoxybutyltributoxysilane,(3,4-epoxycyclohexyl)-methyl-trimethoxysilane,(3,4-epoxycyclohexyl)methyl-triethoxysilane,(3,4-epoxycyclohexyl)methyltripropoxysilane,(3,4-epoxycyclohexyl)-methyl-tributoxysilane,(3,4-epoxycyclohexyl)ethyl-trimethoxysilane,(3,4-epoxycyclohexyl)ethyl-triethoxysilane,(3,4-epoxycyclohexyl)ethyltripropoxysilane,(3,4-epoxycyclohexyl)ethyltributoxysilane,(3,4-epoxycyclohexyl)propyltrimethoxysilane,(3,4-epoxycyclohexyl)propyltriethoxysilane,(3,4-epoxycyclohexyl)propyl-tripropoxysilane,(3,4-epoxycyclohexyl)propyltributoxysilane,(3,4-epoxycyclohexyl)butyltrimethoxysilane, (3,4-epoxycyclohexy)butyltriethoxysilane, (3,4-epoxycyclohexyl)butyltripropoxysilane,(3,4-epoxycyclohexyl)butyltributoxysilane, and so forth.

The particular manner in which the pre-coat is applied to the capacitorbody may vary as desired. In one particular embodiment, the compound isdissolved in an organic solvent and applied to the part as a solution,such as by screen-printing, dipping, electrophoretic coating, spraying,etc. The organic solvent may vary, but is typically an alcohol, such asmethanol, ethanol, etc. Organometallic compounds may constitute fromabout 0.1 wt. % to about 10 wt. %, in some embodiments from about 0.2wt. % to about 8 wt. %, and in some embodiments, from about 0.5 wt. % toabout 5 wt. % of the solution. Solvents may likewise constitute fromabout 90 wt. % to about 99.9 wt. %, in some embodiments from about 92wt. % to about 99.8 wt. %, and in some embodiments, from about 95 wt. %to about 99.5 wt. % of the solution. Once applied, the part may then bedried to remove the solvent therefrom and form a pre-coat containing theorganometallic compound.

D. Solid Electrolyte

As indicated above, a solid electrolyte overlies the dielectric layerand generally functions as the cathode for the capacitor. The solidelectrolyte contains one or more interior layers that overly thedielectric and any optional pre-coat(s), an adhesive film that overliesthe interior layer(s), and one or more outer layers that overly theadhesive film and the interior layer(s).

i. Interior Layer

As indicated, the solid electrolyte contains one or more “inner” layersthat contain a conductive polymer. The term “inner” in this contextrefers to one or more layers that overly the dielectric, whetherdirectly or via another layer (e.g., pre-coat layer). One or multipleinterior layers may be employed. For example, the solid electrolytetypically contains from 2 to 30, in some embodiments from 4 to 20, andin some embodiments, from about 5 to 15 interior layers (e.g., 10layers). The interior layer(s) may, for example, contain a conductivepolymer that is formed from vapor deposition, in situ solution phasepolymerization, pre-polymerized conductive particles, etc. Theconductive polymer is typically Tr-conjugated and has electricalconductivity after oxidation or reduction, such as an electricalconductivity of at least about 1 μS/cm. Examples of such Tr-conjugatedconductive polymers include, for instance, polyheterocycles (e.g.,polypyrroles, polythiophenes, polyanilines, etc.), polyacetylenes,poly-p-phenylenes, polyphenolates, and so forth. In one embodiment, forexample, the polymer is a substituted polythiophene having repeatingunits of the following general formula (I):

wherein,

T is O or S;

D is an optionally substituted C₁ to C₅ alkylene radical (e.g.,methylene, ethylene, n-propylene, n-butylene, n-pentylene, etc.);

R₇ is a linear or branched, C₁ to C₁₈ alkyl radical (e.g., methyl,ethyl, n- or iso-propyl, n-, iso-, sec- or tert-butyl, n-pentyl,1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1-ethylpropyl,1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, n-hexyl,n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl,n-tridecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, etc.); C₅ to C₁₂cycloalkyl radical (e.g., cyclopentyl, cyclohexyl, cycloheptyl,cyclooctyl, cyclononyl, cyclodecyl, etc.); C₆ to C₁₄ aryl radical (e.g.,phenyl, naphthyl, etc.); C₇ to C₁₈ aralkyl radical (e.g., benzyl, o-,m-, p-tolyl, 2,3-, 2,4-, 2,5-, 2-6, 3-4-, 3,5-xylyl, mesityl, etc.); and

q is an integer from 0 to 8, in some embodiments, from 0 to 2, and inone embodiment, 0.

Example of substituents for the radicals “D” or “R₇” include, forinstance, alkyl, cycloalkyl, aryl, aralkyl, alkoxy, halogen, ether,thioether, disulphide, sulfoxide, sulfone, sulfonate, amino, aldehyde,keto, carboxylic acid ester, carboxylic acid, carbonate, carboxylate,cyano, alkylsilane and alkoxysilane groups, carboxylamide groups, and soforth.

Particularly suitable thiophene polymers are those in which “D” is anoptionally substituted C₂ to C₃ alkylene radical. For instance, thepolymer may be optionally substituted poly(3,4-ethylenedioxythiophene),which has repeating units of the following general formula (II):

Such polymers may be formed from using a variety of differenttechniques, such as by in-situ solution polymerization, such asdescribed in U.S. Pat. No. 6,987,663 to Merker, et al. To form such alayer, the precursor monomer may be dissolved in a solvent in thepresence of an oxidative catalyst (e.g., chemically polymerized). Theoxidative catalyst typically includes a transition metal cation, such asiron(III), copper(II), chromium(VI), cerium(IV), manganese(IV),manganese(VII), or ruthenium(III) cations, and etc. A dopant may also beemployed to provide excess charge to the conductive polymer andstabilize the conductivity of the polymer. The dopant typically includesan inorganic or organic anion, such as an ion of a sulfonic acid. Incertain embodiments, the oxidative catalyst has both a catalytic anddoping functionality in that it includes a cation (e.g., transitionmetal) and an anion (e.g., sulfonic acid). For example, the oxidativecatalyst may be a transition metal salt that includes iron(III) cations,such as iron(III) halides (e.g., FeCl₃) or iron(III) salts of otherinorganic acids, such as Fe(ClO₄)₃ or Fe₂(SO₄)₃ and the iron(III) saltsof organic acids and inorganic acids comprising organic radicals.Examples of iron (III) salts of inorganic acids with organic radicalsinclude, for instance, iron(III) salts of sulfuric acid monoesters of C₁to C₂₀ alkanols (e.g., iron(III) salt of lauryl sulfate). Likewise,examples of iron(III) salts of organic acids include, for instance,iron(III) salts of C₁ to C₂₀ alkane sulfonic acids (e.g., methane,ethane, propane, butane, or dodecane sulfonic acid); iron (III) salts ofaliphatic perfluorosulfonic acids (e.g., trifluoromethane sulfonic acid,perfluorobutane sulfonic acid, or perfluorooctane sulfonic acid); iron(III) salts of aliphatic C₁ to C₂₀ carboxylic acids (e.g.,2-ethylhexylcarboxylic acid); iron (III) salts of aliphaticperfluorocarboxylic acids (e.g., trifluoroacetic acid or perfluorooctaneacid); iron (III) salts of aromatic sulfonic acids optionallysubstituted by C₁ to C₂₀ alkyl groups (e.g., benzene sulfonic acid,o-toluene sulfonic acid, p-toluene sulfonic acid, or dodecylbenzenesulfonic acid); iron (III) salts of cycloalkane sulfonic acids (e.g.,camphor sulfonic acid); and so forth. Mixtures of these above-mentionediron(III) salts may also be used. Iron(III)-p-toluene sulfonate,iron(III)-o-toluene sulfonate, and mixtures thereof, are particularlysuitable. One commercially suitable example of iron(III)-p-toluenesulfonate is available from Heraeus under the designation Clevios™ C.

The oxidative catalyst and precursor monomer may be applied eithersequentially or together to initiate the polymerization reaction withinthe solution phase. Suitable application techniques for applying thesecomponents include screen-printing, dipping, electrophoretic coating,and spraying. As an example, the monomer may initially be mixed with theoxidative catalyst to form a precursor solution. Once the mixture isformed, it may be applied to the capacitor element and then allowed topolymerize so that a conductive coating is formed on the surface.Alternatively, the oxidative catalyst and monomer may be appliedsequentially. In one embodiment, for example, the oxidative catalyst isdissolved in an organic solvent (e.g., butanol) and then applied as adipping solution. The part may then be dried to remove the solventtherefrom. Thereafter, the part may be dipped into a solution containingthe monomer. Regardless, polymerization is typically performed attemperatures of from about −10° C. to about 250° C., and in someembodiments, from about 0° C. to about 200° C., depending on theoxidizing agent used and desired reaction time.

Besides in situ solution phase polymerization, the additional exteriorconductive polymer layer(s) may also be formed in other ways. Forexample, one or more of such layers may be formed from pre-polymerizedintrinsically and/or extrinsically conductive polymer particles. Onebenefit of employing such particles is that they can minimize thepresence of ionic species (e.g., Fe²⁺ or Fe³⁺) produced duringconventional in situ polymerization processes, which can causedielectric breakdown under high electric field due to ionic migration.Thus, by applying the conductive polymer as pre-polymerized particlesrather through in situ polymerization, the resulting capacitor mayexhibit a relatively high “breakdown voltage.” In one particularembodiment, for example, the outer layer(s) are formed primarily fromsuch conductive polymer particles in that they constitute about 50 wt. %or more, in some embodiments about 70 wt. % or more, and in someembodiments, about 90 wt. % or more (e.g., 100 wt. %) of a respectiveouter layer.

The particles are typically formed from a 7-conjugated conductivepolymer as described above, such as a polyheterocycle (e.g.,polypyrrole, polythiophene, polyaniline, etc.), polyacetylene,poly-p-phenylene, polyphenolate, and so forth.Poly(3,4-ethylenedioxythiopene) (“PEDT”) and derivatives thereof may beparticularly suitable. If desired, a separate counterion may be employedthat is not covalently bound to the polymer. The counterion may be amonomeric or polymeric anion that counteracts the charge of theconductive polymer. Polymeric anions can, for example, be anions ofpolymeric carboxylic acids (e.g., polyacrylic acids, polymethacrylicacid, polymaleic acids, etc.); polymeric sulfonic acids (e.g.,polystyrene sulfonic acids (“PSS”), polyvinyl sulfonic acids, etc.); andso forth. The acids may also be copolymers, such as copolymers of vinylcarboxylic and vinyl sulfonic acids with other polymerizable monomers,such as acrylic acid esters and styrene. Likewise, suitable monomericanions include, for example, anions of C₁ to C₂₀ alkane sulfonic acids(e.g., dodecane sulfonic acid); aliphatic perfluorosulfonic acids (e.g.,trifluoromethane sulfonic acid, perfluorobutane sulfonic acid orperfluorooctane sulfonic acid); aliphatic C₁ to C₂₀ carboxylic acids(e.g., 2-ethyl-hexylcarboxylic acid); aliphatic perfluorocarboxylicacids (e.g., trifluoroacetic acid or perfluorooctanoic acid); aromaticsulfonic acids optionally substituted by C₁ to C₂₀ alkyl groups (e.g.,benzene sulfonic acid, o-toluene sulfonic acid, p-toluene sulfonic acidor dodecylbenzene sulfonic acid); cycloalkane sulfonic acids (e.g.,camphor sulfonic acid or tetrafluoroborates, hexafluorophosphates,perchlorates, hexafluoroantimonates, hexafluoroarsenates orhexachloroantimonates); and so forth. Particularly suitablecounteranions are polymeric anions, such as a polymeric carboxylic orsulfonic acid (e.g., polystyrene sulfonic acid (“PSS”)). The molecularweight of such polymeric anions typically ranges from about 1,000 toabout 2,000,000, and in some embodiments, from about 2,000 to about500,000.

Regardless of the particular nature of the polymer, the conductivepolymer particles used to form the interior layer(s) typically have anaverage size (e.g., diameter) of from about 1 to about 80 nanometers, insome embodiments from about 2 to about 70 nanometers, and in someembodiments, from about 3 to about 60 nanometers. The diameter of theparticles may be determined using known techniques, such as byultracentrifuge, laser diffraction, etc. The shape of the particles maylikewise vary. In one particular embodiment, for instance, the particlesare spherical in shape. However, it should be understood that othershapes are also contemplated by the present invention, such as plates,rods, discs, bars, tubes, irregular shapes, etc.

Although not necessarily required, the conductive polymer particles maybe applied in the form of a dispersion. The concentration of theconductive polymer in the dispersion may vary depending on the desiredviscosity of the dispersion and the particular manner in which thedispersion is to be applied to the capacitor element. Typically,however, the polymer constitutes from about 0.1 to about 10 wt. %, insome embodiments from about 0.4 to about 5 wt. %, and in someembodiments, from about 0.5 to about 4 wt. % of the dispersion. Thedispersion may also contain one or more components to enhance theoverall properties of the resulting solid electrolyte. For example, thedispersion may contain a binder to further enhance the adhesive natureof the polymeric layer and also increase the stability of the particleswithin the dispersion. The binder may be organic in nature, such aspolyvinyl alcohols, polyvinyl pyrrolidones, polyvinyl chlorides,polyvinyl acetates, polyvinyl butyrates, polyacrylic acid esters,polyacrylic acid amides, polymethacrylic acid esters, polymethacrylicacid amides, polyacrylonitriles, styrene/acrylic acid ester, vinylacetate/acrylic acid ester and ethylene/vinyl acetate copolymers,polybutadienes, polyisoprenes, polystyrenes, polyethers, polyesters,polycarbonates, polyurethanes, polyamides, polyimides, polysulfones,melamine formaldehyde resins, epoxide resins, silicone resins orcelluloses. Dispersion agents may also be employed to facilitate theability to apply the layer to the capacitor element. Suitable dispersionagents include solvents, such as aliphatic alcohols (e.g., methanol,ethanol, i-propanol and butanol), aliphatic ketones (e.g., acetone andmethyl ethyl ketones), aliphatic carboxylic acid esters (e.g., ethylacetate and butyl acetate), aromatic hydrocarbons (e.g., toluene andxylene), aliphatic hydrocarbons (e.g., hexane, heptane and cyclohexane),chlorinated hydrocarbons (e.g., dichloromethane and dichloroethane),aliphatic nitriles (e.g., acetonitrile), aliphatic sulfoxides andsulfones (e.g., dimethyl sulfoxide and sulfolane), aliphatic carboxylicacid amides (e.g., methylacetamide, dimethylacetamide anddimethylformamide), aliphatic and araliphatic ethers (e.g., diethyletherand anisole), water, and mixtures of any of the foregoing solvents. Aparticularly suitable dispersion agent is water.

In addition to those mentioned above, still other ingredients may alsobe used in the dispersion. For example, conventional fillers may be usedthat have a size of from about 10 nanometers to about 100 micrometers,in some embodiments from about 50 nanometers to about 50 micrometers,and in some embodiments, from about 100 nanometers to about 30micrometers. Examples of such fillers include calcium carbonate,silicates, silica, calcium or barium sulfate, aluminum hydroxide, glassfibers or bulbs, wood flour, cellulose powder carbon black, electricallyconductive polymers, etc. The fillers may be introduced into thedispersion in powder form, but may also be present in another form, suchas fibers.

Surface-active substances may also be employed in the dispersion, suchas ionic or non-ionic surfactants. Furthermore, adhesives may beemployed, such as organofunctional silanes or their hydrolysates, forexample 3-glycidoxypropyltrialkoxysilane, 3-aminopropyl-triethoxysilane,3-mercaptopropyl-trimethoxysilane, 3-metacryloxypropyltrimethoxysilane,vinyltrimethoxysilane or octyltriethoxysilane. The dispersion may alsocontain additives that increase conductivity, such as ethergroup-containing compounds (e.g., tetrahydrofuran), lactonegroup-containing compounds (e.g., γ-butyrolactone or γ-valerolactone),amide or lactam group-containing compounds (e.g., caprolactam,N-methylcaprolactam, N,N-dimethylacetamide, N-methylacetamide,N,N-dimethylformamide (DMF), N-methylformamide, N-methylformanilide,N-methylpyrrolidone (NMP), N-octylpyrrolidone, or pyrrolidone), sulfonesand sulfoxides (e.g., sulfolane (tetramethylenesulfone) ordimethylsulfoxide (DMSO)), sugar or sugar derivatives (e.g., saccharose,glucose, fructose, or lactose), sugar alcohols (e.g., sorbitol ormannitol), furan derivatives (e.g., 2-furancarboxylic acid or3-furancarboxylic acid), an alcohols (e.g., ethylene glycol, glycerol,di- or triethylene glycol).

The dispersion may be applied using a variety of known techniques, suchas by spin coating, impregnation, pouring, dropwise application,injection, spraying, doctor blading, brushing, printing (e.g., ink-jet,screen, or pad printing), or dipping. The viscosity of the dispersion istypically from about 0.1 to about 100,000 mPas (measured at a shear rateof 100 s⁻¹), in some embodiments from about 1 to about 10,000 mPas, insome embodiments from about 10 to about 1,500 mPas, and in someembodiments, from about 100 to about 1000 mPas.

ii. Adhesion Film

As indicated above, an adhesive film overlies the interior layer(s) andis formed from sequential chemical vapor deposition, such as by atomiclayer deposition (ALD), molecular layer deposition (MLD), etc. Suchprocesses typically involve the polymerization of a precursor gaseouscompound to form a conductive polymer coating in situ on the capacitor.The precursor compound may be provided in a gaseous state, which is thenpolymerized in situ to deposit the conductive polymer coating. Theprecursor compound may also be provided in a liquid or solid state, inwhich case it is generally vaporized into a gaseous compound and thenpolymerized in situ to deposit the coating. Regardless, a capacitorelement containing one or more interior conductive polymer layers may beinitially exposed to the gaseous precursor compound so that it reactsand bonds to the exposed surface without fully decomposing. Thereafter,a co-reactant (e.g., oxidant) may be exposed to the growth surface whereit reacts with the deposited precursor compound. Once the reaction iscomplete, any remaining vapor byproducts may be removed (e.g., with aninert gas) and the capacitor element may then be subjected to additionalsequential reaction cycles to achieve the target film thickness. Onebenefit of such a process is that the half-reactions are self-limiting.Namely, once the precursor compound has reacted with sites preparedduring a previous co-reactant exposure, the surface reaction will stopbecause the surface sites prepared by the precursor reaction arereactive to the co-reactant, but not the precursor compound itself. Thismeans that during steady state growth, the precursor compound willtypically deposit at most only one monolayer (e.g., molecular fragment)during each half-reaction cycle even when the surface is exposed to thereactant species for a substantial period of time. Among other things,this allows the formation of a thin film coating that is conformal overthe entire surface of the interior layer(s), which in turn, can improvevarious properties of the capacitor.

The precursor compound may vary depending on the type of conductivepolymer that is employed within the adhesive film. Suitable conductivepolymers include, for instance, π-conjugated conductive polymers, suchas a polyheterocycle (e.g., polypyrrole, polythiophene, polyaniline,etc.), polyacetylene, poly-p-phenylene, polyphenolate, and so forth. Inone embodiment, for instance, the precursor compound is a pyrrolecompound having the following general structure:

wherein,

R₁ is hydrogen, alkyl, alkenyl, alkoxy, alkanoyl, alkythio, aryloxy,alkylthioalkyl, alkylaryl, arylalkyl, amino, alkylamino, dialkylamino,aryl, alkylsulfinyl, alkoxyalkyl, alkylsulfonyl, arylthio, arylsulfinyl,alkoxycarbonyl, arylsulfonyl, acrylic acid, phosphoric acid, phosphonicacid, halogen, nitro, cyano, hydroxyl, epoxy, silane, siloxane, alcohol,benzyl, carboxylate, ether, amidosulfonate, ether carboxylate, ethersulfonate, ester sulfonate, urethane, etc.; or both R₁ groups togethermay form an alkylene or alkenylene chain completing a 3, 4, 5, 6, or7-membered aromatic or alicyclic ring, which ring may optionally includeone or more divalent nitrogen, sulfur or oxygen atoms; and

R₂ is hydrogen, alkyl, alkenyl, aryl, alkanoyl, alkylthioalkyl,alkylaryl, arylalkyl, amino, epoxy, silane, siloxane, alcohol, benzyl,carboxylate, ether, ether carboxylate, ether sulfonate, ester sulfonate,urethane, etc. In one particular embodiment, both R₁ and R₂ may behydrogen such that the compound is pyrrole.

In another embodiment, the precursor compound may be an aniline compoundhaving the following general structure:

wherein,

R₅ is independently hydrogen, alkyl, alkenyl, aryl, alkanoyl,alkylthioalkyl, alkylaryl, arylalkyl, amino, epoxy, silane, siloxane,alcohol, benzyl, carboxylate, ether, ether carboxylate, ether sulfonate,ester sulfonate, urethane, etc. In one particular embodiment, each R₅ isan alkyl group (e.g., methyl) or alkoxy group (e.g., methoxy).

Thiophene precursor compounds may also be employed in the adhesive film,such as those having the following general structure:

wherein,

T is O or S;

D is an optionally substituted C₁ to C₅ alkylene radical (e.g.,methylene, ethylene, n-propylene, n-butylene, n-pentylene, etc.);

R₇ is a linear or branched, C₁ to C₁₈ alkyl radical (e.g., methyl,ethyl, n- or iso-propyl, n-, iso-, sec- or tert-butyl, n-pentyl,1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1-ethylpropyl,1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, n-hexyl,n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl,n-tridecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, etc.); C₅ to C₁₂cycloalkyl radical (e.g., cyclopentyl, cyclohexyl, cycloheptyl,cyclooctyl, cyclononyl, cyclodecyl, etc.); C₆ to C₁₄ aryl radical (e.g.,phenyl, naphthyl, etc.); C₇ to C₁₈ aralkyl radical (e.g., benzyl, o-,m-, p-tolyl, 2,3-, 2,4-, 2,5-, 2-6, 3-4-, 3,5-xylyl, mesityl, etc.); and

q is an integer from 0 to 8, in some embodiments, from 0 to 2, and inone embodiment, 0.

Example of substituents for the radicals “D” or “R₇” include, forinstance, alkyl, cycloalkyl, aryl, aralkyl, alkoxy, halogen, ether,thioether, disulphide, sulfoxide, sulfone, sulfonate, amino, aldehyde,keto, carboxylic acid ester, carboxylic acid, carbonate, carboxylate,cyano, alkylsilane and alkoxysilane groups, carboxylamide groups, and soforth.

Particularly suitable thiophene polymers are those in which “D” is anoptionally substituted C₂ to C₃ alkylene radical. For instance, thepolymer may be optionally substituted poly(3,4-ethylenedioxythiophene),which has the following general structure:

For instance, “q” is 0 and the precursor compound is3,4-ethylenedioxthiophene. In yet another embodiment, “q” may be 1 andR₇ may have the structure R—Z⁻X⁺, wherein:R is (CH₂)_(a)—O—(CH₂)_(b)

a is from 0 to 10, in some embodiments from 0 to 6, and in someembodiments, from 1 to 4 (e.g., 1);

b is from 1 to 18, in some embodiments from 1 to 10, and in someembodiments, from 2 to 6 (e.g., 2, 3, 4, or 5);

Z is an anion, such as SO₃ ⁻, C(O)O⁻, BF₄ ⁻, CF₃SO₃ ⁻, SbF₆ ⁻,N(SO₂CF₃)₂ ⁻, C₄H₃O₄ ⁻, ClO₄ ⁻, etc.;

X is a cation, such as hydrogen, an alkali metal (e.g., lithium, sodium,rubidium, cesium or potassium), ammonium, etc. In one embodiment, forinstance, Z may be SO₃, a is 1, b is 3 or 4, and/or X is sodium orpotassium.

The co-reactant may also vary depending on the particular type ofreaction involved for forming the adhesive film. Typically, however, theco-reactant is an oxidizing agent that is capable of oxidizing theprecursor compound (e.g., 3,4-ethylenedioxythiophene) and/or doping aformed polymer so that is converted from a neutral to conductive state.Examples of suitable oxidizing agents for this purpose may include, forinstance, CuCl₂, FeCl₃, FeBr₃, I₂, POBr₃, GeCl₄, SbI₃, Br₂, SbF₅, SbCl₅,TiCl₄, POCl₃, SO₂Cl₂, CrO₂Cl₂, S₂Cl, O(CH₃)₃SbCl₆, VCl₄, VOCl₃, BF₃,(CH₃(CH₂)₃)₂O.BF₃, (C₂H₅)₃O(BF₄), MoCl₅, BF₃.O(C₂H₅)₂ etc. In certainembodiments, it is desirable to employ a volatile oxidizing agent thathas a relatively low boiling temperature so that the reactiontemperatures can be maintained at a relatively level. For example, theoxidizing agent may have a boiling temperature of about 320° C. or less,in some embodiments about 310° C. or less, and in some embodiments, fromabout 220° C. to about 280° C. One particularly suitable volatileoxidizing agent is MoCl₅, which has a boiling temperature of about 268°C.

To deposit the adhesive film, it is generally desirable to subject thecapacitor element containing an interior conductive polymer layer tomultiple cycles within a reactor vessel. For instance, in a typicalreaction cycle, a gaseous precursor compound may be supplied to areactor vessel and allowed to react with the exposed surface of theinterior conductive polymer layer. A gaseous oxidizing agent may then besupplied to the vessel and allowed to oxidize the deposited precursorcompound. Additional cycles may then be repeated to polymerize and/ordope the resulting conductive polymer to achieve the target thickness,which is typically about 10 nanometers or more, in some embodiments fromabout 20 nanometers to about 1,000 nanometers, and in some embodiments,from about 30 nanometers to about 800 nanometers, and in someembodiments, from about 40 nanometers to about 500 nanometers.

In one embodiment, for instance, a reaction cycle is initiated by firstheating the capacitor element to a certain deposition temperature.Although the particular deposition temperature for a given reactioncycle can vary based on a variety of factors, one particular benefit ofthe technique employed in the present invention is that relatively lowtemperatures can be employed. For example, the deposition temperaturemay be about 200° C. or less, in some embodiments about 175° C. or less,and in some embodiments, from about 100° C. to about 160° C. (e.g.,about 150° C.). The reactor vessel pressure during deposition is alsotypically from about 0.01 to about 5 Torr, in some embodiments fromabout 0.1 to about 3 Torr, and in some embodiments, from about 0.3 toabout 2 Torr (e.g., about 1 Torr). While the capacitor element ismaintained at the deposition temperature and pressure, the gas precursorcompound may be supplied to the reactor vessel via an inlet for acertain deposition time period and at a certain flow rate. The gasprecursor flow rate can vary, but is typically from about 1 standardcubic centimeter per minute to about 1 liter per minute. After reactingwith the surface of the capacitor element, an inert gas (e.g., nitrogen,argon, helium, etc.) may be supplied to the reactor vessel to purge itfrom gases and vapor byproducts. A gaseous oxidizing agent may then besupplied to the reactor vessel through an inlet, which may be the sameor different than the inlet used for the precursor compound. Theoxidizing gas flow rate can vary, but is typically between about 1standard cubic centimeter per minute to about 1 standard liter perminute. The temperature and/or pressure within the reaction vesselduring deposition of the precursor compound and oxidizing agent may bethe same or different, but is typically within the ranges noted above.As a result of a reaction cycle, such as described above, one ormultiple layers of the conductive polymer can form near the interfacewith the interior conductive polymer layer(s) and thus, are referred toherein as “interfacial” layer(s). As noted above, additional layers canalso be formed on these interfacial layer(s) by utilizing one or moreadditional reaction cycles during which a precursor compound andoxidizing agent are sequentially supplied and react on the surface.

Various known vapor deposition systems may generally be employed tosequentially form the adhesive film of the present invention. Referringto FIG. 2, for instance, one embodiment of a suitable vapor depositionsystem is shown that is described in more detail in U.S. Pat. No.8,012,261 to Sneh, which is incorporated herein in its entirety byreference thereto. More particularly, the system includes a reactorvessel 200 that contains sidewalls 221 and a top 222 that togetherdefine a gas distribution chamber 201 that is capable of supplying agaseous compound to a deposition chamber 203 via a flow-restrictingelement 202 (e.g., nozzle array). A capacitor element 204 containing oneor more interior conductive polymer layers may be positioned on asubstrate holder 205, which is typically made from a thermallyconductive material, such as tungsten, molybdenum, aluminum, nickel,etc. The holder 205 may be heated so that the capacitor element 204 iscapable of reaching the desired temperature during a reaction cycle. Agas inlet 214 is provided to supply the precursor compound and/oroxidizing agent to the reactor vessel 200 via a line 219. If desired, abooster chamber 216 may be employed in combination with a shut-off valve217 and a purge-exhaust shut-off valve 218. Also, a thermal barrier 220may be employed to inhibit thermal conductance between the sidewalls 221and the top 222. If desired, a draw gas may be employed to help purgegases from the reactor vessel when desired. For instance, gases may flowfrom the deposition chamber 203 into a draw control chamber 208 and to avacuum port 210. A draw gas flows through a draw-gas line 211,draw-source shut-off valve 212, and draw-source line 213 through thedraw control chamber 208 to manage a draw pressure in the draw controlchamber 208.

Regardless of the particular manner in which it is formed, the resultingadhesive film typically has a high intrinsic conductivity. Theconductivity of the film may, for example, may be about 100 S/cm ormore, in some embodiments about 500 S/cm or more, in some embodimentsabout 1,000 S/cm or more, and in some embodiments, from about 1,200 toabout 8,000 S/cm, as determined at a temperature of about 25° C.

iii. Exterior Layer

As noted above, one or more additional exterior layers are also presentin the solid electrolyte that overly the adhesive film. For example, thesolid electrolyte may contain from 2 to 30, in some embodiments from 3to 25, and in some embodiments, from about 4 to 20 exterior layers.Regardless of the number of layers employed, the resulting solidelectrolyte, including all of the interior layer(s) and outer layer(s),typically has a total a thickness of from about 1 micrometer (μm) toabout 200 μm, in some embodiments from about 2 μm to about 50 μm, and insome embodiments, from about 3 μm to about 30 μm.

The exterior layers are generally formed from a 7-conjugated conductivepolymer as described above, such as a polyheterocycle (e.g.,polypyrrole, polythiophene, polyaniline, etc.), polyacetylene,poly-p-phenylene, polyphenolate, and so forth.Poly(3,4-ethylenedioxythiopene) (“PEDT”) and derivatives thereof may beparticularly suitable. Such exterior polymer layer(s) may be formedusing any technique, such as by sequential vapor deposition, in-situsolution polymerization, pre-polymerized particles, etc. In oneembodiment, for instance, the exterior layer(s) may contain one or morelayers formed from pre-polymerized conductive polymer particles such asdescribed above (e.g., dispersion of extrinsically conductive polymerparticles). The exterior layer(s) may be able to further penetrate intothe edge region of the capacitor body to increase the adhesion to thedielectric and result in a more mechanically robust part, which mayreduce equivalent series resistance and leakage current. Because it isgenerally intended to improve the degree of edge coverage rather toimpregnate the interior of the capacitor element, the particles used inthe external layer(s) typically have a larger size than those optionallyemployed in the interior layer(s). For example, the ratio of the averagesize of the particles employed in the exterior layer(s) to the averagesize of the particles employed in the interior layer(s) is typicallyfrom about 1.5 to about 30, in some embodiments from about 2 to about20, and in some embodiments, from about 5 to about 15. For example, theparticles employed in the dispersion of the exterior layer(s) may havean average size of from about 80 to about 500 nanometers, in someembodiments from about 90 to about 250 nanometers, and in someembodiments, from about 100 to about 200 nanometers.

If desired, a crosslinking agent may also be employed in to enhance thedegree of adhesion. When employed, such crosslinking agents are appliedprior to application of the dispersion used in the exterior layer(s).Suitable crosslinking agents are described, for instance, in U.S. PatentPublication No. 2007/0064376 to Merker, et al. and include, forinstance, amines (e.g., diamines, triamines, oligomer amines,polyamines, etc.); polyvalent metal cations, such as salts or compoundsof Mg, Al, Ca, Fe, Cr, Mn, Ba, Ti, Co, Ni, Cu, Ru, Ce or Zn, phosphoniumcompounds, sulfonium compounds, etc. Particularly suitable examplesinclude, for instance, 1,4-diaminocyclohexane,1,4-bis(amino-methyl)cyclohexane, ethylenediamine, 1,6-hexanediamine,1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine,1,10-decanediamine, 1,12-dodecanediamine, N,N-dimethylethylenediamine,N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetramethyl-1,4-butanediamine, etc., as well as mixturesthereof. The crosslinking agent is typically applied from a solution ordispersion whose pH is from 1 to 10, in some embodiments from 2 to 7, insome embodiments, from 3 to 6, as determined at 25° C. Acidic compoundsmay be employed to help achieve the desired pH level. Examples ofsolvents or dispersants for the crosslinking agent include water ororganic solvents, such as alcohols, ketones, carboxylic esters, etc. Thecrosslinking agent may be applied to the capacitor body by any knownprocess, such as spin-coating, impregnation, casting, dropwiseapplication, spray application, vapor deposition, sputtering,sublimation, knife-coating, painting or printing, for example inkjet,screen or pad printing. Once applied, the crosslinking agent may bedried prior to application of the polymer dispersion. This process maythen be repeated until the desired thickness is achieved. For example,the total thickness of the entire external polymer coating, includingthe crosslinking agent and dispersion layers, may range from about 1 toabout 50 μm, in some embodiments from about 2 to about 40 μm, and insome embodiments, from about 5 to about 20 μm.

Of course, in certain embodiments, the enhanced adhesion provided by thesequential vapor-deposited adhesive film may eliminate the need for suchcrosslinking agents. In fact, in certain embodiments, the capacitor maybe free of crosslinking agents.

E. Other Components

The capacitor may also employ a cathode coating that overlies the solidelectrolyte. The cathode coating may contain a metal particle layerincludes a plurality of conductive metal particles dispersed within aresinous polymer matrix. The particles typically constitute from about50 wt. % to about 99 wt. %, in some embodiments from about 60 wt. % toabout 98 wt. %, and in some embodiments, from about 70 wt. % to about 95wt. % of the layer, while the resinous polymer matrix typicallyconstitutes from about 1 wt. % to about 50 wt. %, in some embodimentsfrom about 2 wt. % to about 40 wt. %, and in some embodiments, fromabout 5 wt. % to about 30 wt. % of the layer.

The conductive metal particles may be formed from a variety of differentmetals, such as copper, nickel, silver, nickel, zinc, tin, lead, copper,aluminum, molybdenum, titanium, iron, zirconium, magnesium, etc., aswell as alloys thereof. Silver is a particularly suitable conductivemetal for use in the layer. The metal particles often have a relativelysmall size, such as an average size of from about 0.01 to about 50micrometers, in some embodiments from about 0.1 to about 40 micrometers,and in some embodiments, from about 1 to about 30 micrometers.Typically, only one metal particle layer is employed, although it shouldbe understood that multiple layers may be employed if so desired. Thetotal thickness of such layer(s) is typically within the range of fromabout 1 μm to about 500 μm, in some embodiments from about 5 μm to about200 μm, and in some embodiments, from about 10 μm to about 100 μm.

The resinous polymer matrix typically includes a polymer, which may bethermoplastic or thermosetting in nature. Typically, however, thepolymer is selected so that it can act as a barrier to electromigrationof silver ions, and also so that it contains a relatively small amountof polar groups to minimize the degree of water adsorption in thecathode coating. In this regard, the present inventors have found thatvinyl acetal polymers are particularly suitable for this purpose, suchas polyvinyl butyral, polyvinyl formal, etc. Polyvinyl butyral, forinstance, may be formed by reacting polyvinyl alcohol with an aldehyde(e.g., butyraldehyde). Because this reaction is not typically complete,polyvinyl butyral will generally have a residual hydroxyl content. Byminimizing this content, however, the polymer can possess a lesserdegree of strong polar groups, which would otherwise result in a highdegree of moisture adsorption and result in silver ion migration. Forinstance, the residual hydroxyl content in polyvinyl acetal may be about35 mol. % or less, in some embodiments about 30 mol. % or less, and insome embodiments, from about 10 mol. % to about 25 mol. %. Onecommercially available example of such a polymer is available fromSekisui Chemical Co., Ltd. under the designation “BH-S” (polyvinylbutyral).

To form the cathode coating, a conductive paste is typically applied tothe capacitor that overlies the solid electrolyte. One or more organicsolvents are generally employed in the paste. A variety of differentorganic solvents may generally be employed, such as glycols (e.g.,propylene glycol, butylene glycol, triethylene glycol, hexylene glycol,polyethylene glycols, ethoxydiglycol, and dipropyleneglycol); glycolethers (e.g., methyl glycol ether, ethyl glycol ether, and isopropylglycol ether); ethers (e.g., diethyl ether and tetrahydrofuran);alcohols (e.g., benzyl alcohol, methanol, ethanol, n-propanol,iso-propanol, and butanol); triglycerides; ketones (e.g., acetone,methyl ethyl ketone, and methyl isobutyl ketone); esters (e.g., ethylacetate, butyl acetate, diethylene glycol ether acetate, andmethoxypropyl acetate); amides (e.g., dimethylformamide,dimethylacetamide, dimethylcaprylic/capric fatty acid amide andN-alkylpyrrolidones); nitriles (e.g., acetonitrile, propionitrile,butyronitrile and benzonitrile); sulfoxides or sulfones (e.g., dimethylsulfoxide (DMSO) and sulfolane); etc., as well as mixtures thereof. Theorganic solvent(s) typically constitute from about 10 wt. % to about 70wt. %, in some embodiments from about 20 wt. % to about 65 wt. %, and insome embodiments, from about 30 wt. % to about 60 wt. %. of the paste.Typically, the metal particles constitute from about 10 wt. % to about60 wt. %, in some embodiments from about 20 wt. % to about 45 wt. %, andin some embodiments, from about 25 wt. % to about 40 wt. % of the paste,and the resinous polymer matrix constitutes from about 0.1 wt. % toabout 20 wt. %, in some embodiments from about 0.2 wt. % to about 10 wt.%, and in some embodiments, from about 0.5 wt. % to about 8 wt. % of thepaste.

The paste may have a relatively low viscosity, allowing it to be readilyhandled and applied to a capacitor element. The viscosity may, forinstance, range from about 50 to about 3,000 centipoise, in someembodiments from about 100 to about 2,000 centipoise, and in someembodiments, from about 200 to about 1,000 centipoise, such as measuredwith a Brookfield DV-1 viscometer (cone and plate) operating at a speedof 10 rpm and a temperature of 25° C. If desired, thickeners or otherviscosity modifiers may be employed in the paste to increase or decreaseviscosity. Further, the thickness of the applied paste may also berelatively thin and still achieve the desired properties. For example,the thickness of the paste may be from about 0.01 to about 50micrometers, in some embodiments from about 0.5 to about 30 micrometers,and in some embodiments, from about 1 to about 25 micrometers. Onceapplied, the metal paste may be optionally dried to remove certaincomponents, such as the organic solvents. For instance, drying may occurat a temperature of from about 20° C. to about 150° C., in someembodiments from about 50° C. to about 140° C., and in some embodiments,from about 80° C. to about 130° C.

If desired, the capacitor may also contain other layers as is known inthe art. In certain embodiments, for instance, a carbon layer (e.g.,graphite) may be positioned between the solid electrolyte and the silverlayer that can help further limit contact of the silver layer with thesolid electrolyte.

II. Terminations

Once the layers of the capacitor element are formed, the resultingcapacitor may be provided with terminations. For example, the capacitormay contain an anode termination to which an anode lead of the capacitorelement is electrically connected and a cathode termination to which thecathode of the capacitor is electrically connected. Any conductivematerial may be employed to form the terminations, such as a conductivemetal (e.g., copper, nickel, silver, nickel, zinc, tin, palladium, lead,copper, aluminum, molybdenum, titanium, iron, zirconium, magnesium, andalloys thereof). Particularly suitable conductive metals include, forinstance, copper, copper alloys (e.g., copper-zirconium,copper-magnesium, copper-zinc, or copper-iron), nickel, and nickelalloys (e.g., nickel-iron). The thickness of the terminations isgenerally selected to minimize the thickness of the capacitor. Forinstance, the thickness of the terminations may range from about 0.05 toabout 1 millimeter, in some embodiments from about 0.05 to about 0.5millimeters, and from about 0.07 to about 0.2 millimeters. One exemplaryconductive material is a copper-iron alloy metal plate available fromWieland (Germany). If desired, the surface of the terminations may beelectroplated with nickel, silver, gold, tin, etc. as is known in theart to ensure that the final part is mountable to the circuit board. Inone particular embodiment, both surfaces of the terminations are platedwith nickel and silver flashes, respectively, while the mounting surfaceis also plated with a tin solder layer.

The terminations may be connected to the capacitor element using anytechnique known in the art. In one embodiment, for example, a lead framemay be provided that defines the cathode termination and anodetermination. To attach the electrolytic capacitor element to the leadframe, a conductive adhesive may initially be applied to a surface ofthe cathode termination. The conductive adhesive may include, forinstance, conductive metal particles contained with a resin composition.The metal particles may be silver, copper, gold, platinum, nickel, zinc,bismuth, etc. The resin composition may include a thermoset resin (e.g.,epoxy resin), curing agent (e.g., acid anhydride), and compound (e.g.,silane compounds). Suitable conductive adhesives may be described inU.S. Patent Application Publication No. 2006/0038304 to Osako, et al.Any of a variety of techniques may be used to apply the conductiveadhesive to the cathode termination. Printing techniques, for instance,may be employed due to their practical and cost-saving benefits. Theanode lead may also be electrically connected to the anode terminationusing any technique known in the art, such as mechanical welding, laserwelding, conductive adhesives, etc. Upon electrically connecting theanode lead to the anode termination, the conductive adhesive may then becured to ensure that the electrolytic capacitor element is adequatelyadhered to the cathode termination.

Referring to FIG. 1, for example, the electrolytic capacitor 30 is shownas including an anode termination 62 and a cathode termination 72 inelectrical connection with the capacitor element 33 having an uppersurface 37, lower surface 39, rear surface 38, and front surface 36.Although it may be in electrical contact with any of the surfaces of thecapacitor element 33, the cathode termination 72 in the illustratedembodiment is in electrical contact with the lower surface 39 via aconductive adhesive. More specifically, the cathode termination 72contains a first component 73 that is in electrical contact andgenerally parallel with the lower surface 39 of the capacitor element33. The cathode termination 72 may also contain a second component 74that is substantially perpendicular to the first component 73 and inelectrical contract with the rear surface 38 of the capacitor element33. The anode termination 62 likewise contains a first component 63positioned substantially perpendicular to a second component 64. Thefirst component 63 is in electrical contact and generally parallel withthe lower surface 39 of the capacitor element 33. The second component64 contains a region 51 that carries an anode lead 16. Although notdepicted in FIG. 1, the region 51 may possess a “U-shape” to furtherenhance surface contact and mechanical stability of the lead 16.

The terminations may be connected to the capacitor element using anytechnique known in the art. In one embodiment, for example, a lead framemay be provided that defines the cathode termination 72 and anodetermination 62. To attach the electrolytic capacitor element 33 to thelead frame, the conductive adhesive may initially be applied to asurface of the cathode termination 72. The conductive adhesive mayinclude, for instance, conductive metal particles contained with a resincomposition. The metal particles may be silver, copper, gold, platinum,nickel, zinc, bismuth, etc. The resin composition may include athermoset resin (e.g., epoxy resin), curing agent (e.g., acidanhydride), and coupling agent (e.g., silane coupling agents). Suitableconductive adhesives may be described in U.S. Patent Publication No.2006/0038304 to Osako, et al. Any of a variety of techniques may be usedto apply the conductive adhesive to the cathode termination 72. Printingtechniques, for instance, may be employed due to their practical andcost-saving benefits.

A variety of methods may generally be employed to attach theterminations to the capacitor. In one embodiment, for example, thesecond component 64 of the anode termination 62 is initially bent upwardto the position shown in FIG. 1. Thereafter, the capacitor element 33 ispositioned on the cathode termination 72 so that its lower surface 39contacts the adhesive and the anode lead 16 is received by the region51. If desired, an insulating material (not shown), such as a plasticpad or tape, may be positioned between the lower surface 39 of thecapacitor element 33 and the first component 63 of the anode termination62 to electrically isolate the anode and cathode terminations.

The anode lead 16 is then electrically connected to the region 51 usingany technique known in the art, such as mechanical welding, laserwelding, conductive adhesives, etc. For example, the anode lead 16 maybe welded to the anode termination 62 using a laser. Lasers generallycontain resonators that include a laser medium capable of releasingphotons by stimulated emission and an energy source that excites theelements of the laser medium. One type of suitable laser is one in whichthe laser medium consist of an aluminum and yttrium garnet (YAG), dopedwith neodymium (Nd). The excited particles are neodymium ions Nd³⁺. Theenergy source may provide continuous energy to the laser medium to emita continuous laser beam or energy discharges to emit a pulsed laserbeam. Upon electrically connecting the anode lead 16 to the anodetermination 62, the conductive adhesive may then be cured. For example,a heat press may be used to apply heat and pressure to ensure that theelectrolytic capacitor element 33 is adequately adhered to the cathodetermination 72 by the adhesive.

III. Housing

Due to the ability of the capacitor to exhibit good electricalperformance in various environments, it is not necessary for thecapacitor element to be hermetically sealed within a housing.Nevertheless, in certain embodiments, it may be desired to hermeticallyseal the capacitor element within a housing. The capacitor element maybe sealed within a housing in various ways. In certain embodiments, forinstance, the capacitor element may be enclosed within a case, which maythen be filled with a resinous material, such as a thermoset resin(e.g., epoxy resin) that can be cured to form a hardened housing.Examples of such resins include, for instance, epoxy resins, polyimideresins, melamine resins, urea-formaldehyde resins, polyurethane resins,phenolic resins, polyester resins, etc. Epoxy resins are alsoparticularly suitable. Still other additives may also be employed, suchas photoinitiators, viscosity modifiers, suspension aiding agents,pigments, stress reducing agents, non-conductive fillers, stabilizers,etc. For example, the non-conductive fillers may include inorganic oxideparticles, such as silica, alumina, zirconia, magnesium oxide, ironoxide, copper oxide, zeolites, silicates, clays (e.g., smectite clay),etc., as well as composites (e.g., alumina-coated silica particles) andmixtures thereof. Regardless, the resinous material may surround andencapsulate the capacitor element so that at least a portion of theanode and cathode terminations are exposed for mounting onto a circuitboard. When encapsulated in this manner, the capacitor element andresinous material form an integral capacitor. As shown in FIG. 1, forinstance, the capacitor element 33 is encapsulated within a housing 28so that a portion of the anode termination 62 and a portion of thecathode termination 72 are exposed.

Of course, in alternative embodiments, it may be desirable to enclosethe capacitor element within a housing that remains separate anddistinct. In this manner, the atmosphere of the housing may be gaseousand contain at least one inert gas, such as nitrogen, helium, argon,xenon, neon, krypton, radon, and so forth, as well as mixtures thereof.Typically, inert gases constitute the majority of the atmosphere withinthe housing, such as from about 50 wt. % to 100 wt. %, in someembodiments from about 75 wt. % to 100 wt. %, and in some embodiments,from about 90 wt. % to about 99 wt. % of the atmosphere. If desired, arelatively small amount of non-inert gases may also be employed, such ascarbon dioxide, oxygen, water vapor, etc. In such cases, however, thenon-inert gases typically constitute 15 wt. % or less, in someembodiments 10 wt. % or less, in some embodiments about 5 wt. % or less,in some embodiments about 1 wt. % or less, and in some embodiments, fromabout 0.01 wt. % to about 1 wt. % of the atmosphere within the housing.Any of a variety of different materials may be used to form the separatehousing, such as metals, plastics, ceramics, and so forth. In oneembodiment, for example, the housing includes one or more layers of ametal, such as tantalum, niobium, aluminum, nickel, hafnium, titanium,copper, silver, steel (e.g., stainless), alloys thereof (e.g.,electrically conductive oxides), composites thereof (e.g., metal coatedwith electrically conductive oxide), and so forth. In anotherembodiment, the housing may include one or more layers of a ceramicmaterial, such as aluminum nitride, aluminum oxide, silicon oxide,magnesium oxide, calcium oxide, glass, etc., as well as combinationsthereof. The housing may have any desired shape, such as cylindrical,D-shaped, rectangular, triangular, prismatic, etc.

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. A method for forming a solid electrolyticcapacitor element, the method comprising: positioning a capacitorelement with a reactor vessel, wherein the capacitor element comprises asintered porous anode body, a dielectric overlying the anode body, andan interior conductive polymer layer overlying the dielectric; forming afilm on the capacitor element by a sequential vapor deposition process,the process including subjecting the capacitor element to a reactioncycle that includes contacting the capacitor element with a gaseousprecursor compound that bonds to a surface of the interior conductivepolymer layer and thereafter contacting the capacitor element with agaseous oxidizing agent to oxidize and/or polymerize the precursorcompound; and applying an exterior conductive polymer layer over thefilm.
 2. The method of claim 1, wherein the precursor compound is apyrrole, aniline, or a thiophene compound.
 3. The method of claim 2,wherein the anode body includes tantalum and the dielectric includestantalum pentoxide.
 4. The method of claim 1, wherein the precursorcompound is 3,4-ethylenedioxythiophene.
 5. The method of claim 1,wherein the oxidizing agent has a boiling temperature of about 320° C.or less.
 6. The method of claim 1, wherein the oxidizing agent is MoCl₅.7. The method of claim 1, wherein the capacitor element is heated to atemperature of about 200° C. or less during the reaction cycle.
 8. Themethod of claim 1, further comprising contacting the capacitor elementwith an inert gas prior to contact with the oxidizing agent.
 9. Themethod of claim 1, further comprising subjecting the capacitor elementto one or more additional reaction cycles that include contacting thecapacitor element with a gaseous precursor compound and thereaftercontacting the capacitor element with a gaseous oxidizing agent.
 10. Themethod of claim 1, wherein the film has a thickness of about 10nanometers or more.
 11. The method of claim 1, wherein the film has anintrinsic conductivity of about 100 S/cm or more as determined at atemperature of about 25° C.
 12. The method of claim 1, wherein thecapacitor element further comprises a pre-coat overlying the dielectric.13. The method of claim 1, wherein the interior conductive polymerlayer, the exterior conductive polymer layer, or both are formed from adispersion of conductive polymer particles.
 14. The method of claim 1,wherein the interior conductive polymer layer is formed by solutionphase polymerization.